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<entry-title>ISO 8601</entry-title>

The International Standards Organisation's standard, number 8601 is an international standard for date and time representations. It is used for all date-time representations in microformats, as well as a number of other formats (Microformats in HTML5 <time> element & datetime attribute, XML Schema Datatypes, RDF, Atom).


Image: XKCD

In addition, ISO 8601 dates in particular are the most globally unambiguously human readable/writeable date format and thus should always be used on the (world wide) web.


The following are good prose overviews of ISO 8601:


microformats in general use a subset of ISO8601 - preferring uses which are more human readable (requiring hyphens in dates, and colons in times).

All date-time properties in microformats use ISO8601 values. E.g.

RFC 3339

RFC 3339 defines a profile of ISO 8601 for the use in Internet protocols and standards.

  • It explicitly excludes durations and dates before the common era.
  • The more complex formats like week numbers and ordinal day are not permitted (see RFC 3339, section 5.6).

ISO 8601 implementations in programming libraries

  • JodaTime - the Java date-time library - ISO8601 Java calendar system
  • Perl: DateTime::Format::ISO8601
  • Ruby 1.9 implements an iso8601 method in the Date STDLIB but it does not handle ordinal dates.
  • Glenn Jones' microformat-node parser includes isodate.js, a Node.js implementation of (some of) ISO 8601.

to do! document more implementations.


  • How should dates before the common era be marked up? Andy Mabbett
    • What are the use-cases? Link to *-examples page? - Tantek
  • If a web page is created or edited by a non-technical human, it is unfriendly to expect them to work in ISO date format. Charles Belov
    • ISO dates are more readable/usable by people globally than any one locale-specific format, thus it is more friendly globally to use and ask humans to edit ISO 8601 dates than asking them to try to read/write all the odd and quirky locale-specific formats. - Tantek

See also

Related pages